1. Field of the Invention
The present invention relates to a rotational coupling device, more specifically but not by way of limitation, a device that facilitates the operable coupling of a shaft with a component such as a gear or pulley disposed within a standard printer.
2. Description of the Related Art
Most printers have disposed therein a plurality of operably connected components such as gears, pulleys and rolls that function to perform a variety of activities. For instance, these components function to move printing media through the print path or to move the printhead in a desired motion. Conventional shafts are routinely operably coupled with at least one gear and/or pulley. These conventional shafts are substantially hollow having a consistent wall thickness to allow for minimal manufacturing times and warp minimization. These shafts routinely use areas known as flats, which are regions in the shaft that have at least two sides. The number of flats disposed on the circumference of the shaft can vary depending on the application. The amount of flats used on shafts can be as few as one or numerous different amounts of flats can be utilized. The flats are generally planar in shape to facilitate the coupling of a gear or pulley having a mateable shape to the shaft.
One problem with utilizing flats is that the flats cannot be disposed substantially along the entire length of the shaft as this type of configuration will interrupt the journal surface at the ends of the shaft. A discontinuous journal surface has been shown to create problems, such as uneven wear, as the shaft rotates and other negative effects such as untimely breakdown of any lubrication or bad acoustics.
Commonly, a shaft disposed within a conventional printer will be supported at the ends by bushings which facilitate rotational coupling with pulleys or rolls outside the bushings. The shafts further require a method of providing a rotational coupling to a gear in the middle of its span. As the shaft must be inserted through the pair of bushings from one direction, this forces the designer to make compromises. More specifically, the bushings are commonly manufactured to be different diameters. This increases the number of parts in the printer. Also, one journal can end up being too small a diameter for strength requirements, and the other too large for friction and cooling requirements. Indeed, the resulting multiple stepping of the shaft diameter can create a problem wherein the diameter is either too small or too large at any of the various rotational and non-rotational interfaces along the shaft.
Accordingly, there is a need for a device that can provide rotational coupling between a shaft and another component that can eliminate the need for or substantially reduce the number of steps required in the shaft. Furthermore, the device should substantially encircle the shaft and be able to be temporarily expanded in order to be traversed across the shaft and secured in the desired location on the shaft. The securing of the device to the shaft should be able to be accomplished without utilization of additional mechanical or chemical methods. Additionally, it is desired that subsequent to the expansion of the device and placement in its desired position along the shaft that the device returns to a shape and size such that the device compresses against the shaft substantially inhibiting any longitudinal movement.